In the outer plexiform layer of the cat retina large field background stimuli are able to enhance the responses of horizontal cells to small red flickering spots. The responses to the spots originate with the red cones; the enhancement effect of the background originates mainly with rods, as demonstrated by spectral sensitivity studies. These results demonstrate a new rod-cone interaction and suggest a different role for the horizontal cell 'feedback' synapse onto cones, at least for these rapid stimuli. In the dark, when horizontal cells are depolarized, an inhibitory transmitter is released onto the cones, reducing the amplitude of response. The light-induced hyperpolarization of horizontal cells releases cones from this inhibition. The mechanism stands in contrast to classic horizontal cell feedback, where horizontal cell hyperpolarization reduces the cone response, but after some delay. The dopaminergic amacrine cells of monkey retina have been studied using immunocytochemical methods. Using an antibody directed aginst tyrosine hydroxylase as a marker, these cells have been seen to receive input from bipolar cells, as well as other amacrine cells, as previously reported. The bipolar appears to be a specific type called 'giant bistratified' and is connected specifically to cones. At the inner margin of the retina, a second type of glial cell, the fibrous astrocyte, has been found to respond electrically to natural photic stimulation. These cells, which are imbedded in the optic nerve fiber layer, respond with transient depolarizations to the onset and cessation of light stimuli. Their responses probably reflect the release of potassium from ganglion cell axons passing through the nerve fiber layer. Previously, Muller cells were the only retinal glial cells known to have light responses.
| Connaughton, V P; Graham, D; Nelson, R (2004) Identification and morphological classification of horizontal, bipolar, and amacrine cells within the zebrafish retina. J Comp Neurol 477:371-85 |
| Kolb, H; Nelson, R; Ahnelt, P et al. (2001) Cellular organization of the vertebrate retina. Prog Brain Res 131:3-26 |
| Nelson, R; Janis, A T; Behar, T N et al. (2001) Physiological responses associated with kainate receptor immunoreactivity in dissociated zebrafish retinal neurons: a voltage probe study. Prog Brain Res 131:255-65 |
| Connaughton, V P; Nelson, R (2000) Axonal stratification patterns and glutamate-gated conductance mechanisms in zebrafish retinal bipolar cells. J Physiol 524 Pt 1:135-46 |
| Nelson, R; Schaffner, A E; Li, Y X et al. (1999) Distribution of GABA(C)-like responses among acutely dissociated rat retinal neurons. Vis Neurosci 16:179-90 |
